Back light module with birefringent crystal assemblies
A back light module (100) includes a light guide plate (130), a number of light sources (110) at one side of the light guide plate, and a number of birefringent crystal assemblies (120) respectively located between the light sources and the side of the light guide plate. Each birefringent crystal assembly includes a generally wedge-shaped first birefringent crystal (121) and a generally wedge-shaped second birefringent crystal (122) adhered to each other back-to-back. The birefringent crystal assembly enlarges a radiation angle of optical beams emitted from the corresponding light source. The optical beams with enlarged radiation angles enter the side of the light guide plate, and help provide excellent uniformity of brightness to an associated liquid crystal display panel.
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1. Field of the Invention
This invention concerns light source systems, and more specifically a back light module typically used in a liquid crystal display (LCD).
2. Description of the Prior Art
Users of portable electronic devices such as laptop and notebook computers, mobile phones and game devices expect the viewing screens of portable electronic devices to be large, clear and bright. Performance equal to that of cathode-ray tube (CRT) desktop monitors is desired. LCDs are one type of flat panel display (FPD) that can satisfy these expectations. However, because liquid crystals in an LCD are not self-luminescent, the LCD needs a back light module that offers sufficient luminance (brightness) for a planar surface.
Referring to
Referring to
Accordingly, an object of the present invention is to provide a back light module which affords excellent uniform brightness for an associated liquid crystal display panel.
To achieve the above object, a back light module of a first preferred embodiment of the present invention includes a light guide plate, a plurality of aligned light sources at one side of the light guide plate, and a plurality of birefringent crystal assemblies respectively located between the light sources and the side of the light guide plate. Each birefringent crystal assembly includes a generally wedge-shaped first birefringent crystal and a generally wedge-shaped second birefringent crystal adhered to each other back-to-back. The birefringent crystal assembly enlarges a radiation angle of light beams emitted from the corresponding light source. The light beams with enlarged radiation angles enter the side of the light guide plate, thereby providing excellent uniformity of brightness for an associated liquid crystal display panel.
These and other features, aspects and advantages of the present invention will become more apparent from the following detailed description and claims, and from the accompanying drawings in which:
For facilitating understanding, like components are designated by like reference numerals throughout the various embodiments of the invention as shown in the various drawing figures.
Reference will now be made to the drawing figures to describe the present invention in detail.
Referring to
The light guide plate 130 is a substantially rectangular plane body, and includes the light incident surface 131, the light-emitting surface 132, a bottom surface 133, and three side surfaces (not labeled). A plurality of reflective dots 134 are formed on or applied on the bottom surface 133, so as to enhance uniform emission of light from the light-emitting surface 132. Further, in order to improve optical efficiency, reflective sheets or films can be attached on the bottom surface 133 and the side surfaces.
Referring also to
Referring to
sin θw=no sin θo1
When the o-ray enters the interface of the second surface 1212 of the first birefringent crystal 121 and the second surface 1221 of the second birefringent crystal 122 (shown in
no sin(θw−θo1)=ne sin θo3
When the o-ray enters the first surface 1222 of the second birefringent crystal 122 (shown in
ne sin(θw−θo3)=sin θo5
Then when the o-ray emits from the birefringent crystal assembly 120, it forms an angle θo6 relative to a plane that is parallel to a bottom surface of the birefringent crystal assembly 120, wherein θo6 is equal to θw minus θo5. Thus, a radiation angle of light beams is enlarged.
Similar to the optical path of the o-ray in the first birefringent crystal 121 and the second birefringent crystal 122, after passing through the birefringent crystal assembly 120, the resulting e-ray also forms an angle relative to the plane that is parallel to the bottom surface of the birefringent crystal assembly 120. Referring to
Referring to
In the present invention, any of the birefringent crystals can be lithium niobate (LiNbO3) or yttrium orthovanadate (YVO4) crystals. The greater the birefringent effect that the birefringent crystal has, the more uniform brightness of the back light module can be. Further, another kind of light source having similar characteristics to those of LEDs can be used instead of the LEDs.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Claims
1. A back light module comprising:
- a light guide plate;
- a plurality of aligned light sources configured for providing light beams at one side of the light guide plate; and
- at least one birefringent crystal assembly located between the light sources and the light guide plate, the birefringent crystal assembly comprising two generally wedge-shaped birefringent crystals adhered to each other and being configured for enlarging a radiation angle of light beams, each of the wedge-shaped birefringent crystals comprising a first surface and a second surface, the first surface being oblique to an incident surface of the light guide plate, the second surface being opposite to the first surface and parallel to the incident surface of the light guide plate, the two second surfaces of the wedge-shaped birefringent crystals adhering to each other.
2. The back light module as described in claim 1 wherein the back light module comprises a plurality of the birefringent crystal assemblies, and a number of the birefringent crystal assemblies is equal to a number of the light sources, each of the light sources corresponds to a respective one of the birefringent crystal assemblies and emits light beams directly to the corresponding birefringent crystal assembly.
3. The back light module as described in claim 1, wherein the birefringent crystals are lithium niobate crystals.
4. The back light module as described in claim 1, wherein the birefringent crystals are yttrium orthovanadate crystals.
5. The back light module as described in claim 1, wherein an angle between optical axes of the two birefringent crystals is substantially 90 degrees.
6. The back light module as described in claim 1, wherein said birefringent crystal assembly is substantially a parallelepiped.
7. The back light module as described in claim 1, wherein the light sources are light emitting diodes.
8. The back light module as described in claim 1, wherein light beams emitted from said point light source enter the incident surface of the light guide plate by penetrating one first surface, the two second surfaces, and the other first surface, in sequence.
9. A back light module comprising:
- a light guide plate;
- at least one point light source located beside said light guide plate;
- at least one light splitting/rejoining device comprising two generally wedge-shaped birefringent crystals adhered to each other, each light splitting/rejoining device being located between said point light source and the light guide plate so as to initially split light and successively rejoin split light before the light enters the light guide plate, of the wedge-shaped birefringent crystals comprising a first surface and a second surface, the first surface being oblique to an incident surface of the light guide plate, the second surface being opposite to the first surface and parallel to the incident surface of the light guide plate, the two second surfaces of the wedge-shaped birefringent crystals adhering to each other.
10. The light module as described in claim 9, wherein said split light includes an O-ray and E-ray.
11. The light module as described in claim 9, wherein each of split light performs an unsymmetrical optical intensity curve with regard to a symmetrical radiation angle range while the rejoin light performs a symmetrical optical intensity curve with regard to the symmetrical radiation angle range.
12. The light module as described in claim 11, wherein the symmetrical light intensity curve is configured to be shorter and fatter than an original intensity curve derived from the point light source which is not affected by said light splitting/rejoining device.
13. The back light module as described in claim 9, wherein light beams emitted from said point light source enter the incident surface of the light guide plate by penetrating one first surface, the two second surfaces, and the other first surface, in sequence.
14. A light module comprising:
- a light guide plate;
- at least one point light source located beside said light guide plate;
- at least one light transforming device comprising two generally wedge-shaped birefringent crystals adhered to each other, each light transforming device being located between said point light source and the light guide plate so as to convert the one point light source into at least two virtual point light sources thus increasing a light radiation angle range by successive refraction, each of the wedge-shaped birefringent crystals comprising a first surface and a second surface, the first surface being oblique to an incident surface of the light guide plate, the second surface being opposite to the first surface and parallel to the incident surface of the light guide plate, the two second surfaces of the wedge-shaped birefringent crystals adhering to each other.
15. The light module as described in claim 14, wherein a maximum light intensity of a transformed light is smaller than that of light which is not affected by said light transforming device.
16. The light module as described in claim 14, wherein light beams emitted from said point light source enter the incident surface of the light guide plate by penetrating one first surface, the two second surface and the other first surface, in sequence.
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Type: Grant
Filed: Aug 2, 2004
Date of Patent: Feb 19, 2008
Patent Publication Number: 20050024848
Assignee: Hon Hai Precision Ind. Co., Ltd. (Taipei Hsien)
Inventors: Chun-Yu Lee (Tu-Chen), Jen-Tsorng Chang (Tu-Chen)
Primary Examiner: Jong-Suk (James) Lee
Assistant Examiner: Jacob Y Choi
Attorney: Wei Te Chung
Application Number: 10/910,385
International Classification: F21V 9/14 (20060101);